The requirements are not onerous, it is the basic preemption of monopolist behavior.
Qualifying "random apps" is something that is a true challenge, but that holds regardless of the API being offered — the problem is that Apple saves some programming API only for themselves, instead of introducing acceptable & objective market terms to be met (if deemed unsafe, they could require companies to demonstrate compliance with things like CRA to get access to these APIs).
Many Europeans are upset that Apple blames Europe that they cannot implement this because it would sacrifice privacy. (Which is kind of ironic, because the EU has nearly the best privacy protection worldwide.)
Apple doesn't care about privacy. By default (without ADP), your (i)Messages, Drive files, contacts, calendars, backups of data from third-party apps are not end-to-end encrypted [1]. US law enforcement can request it. EU citizens are not protected because the US can use the CLOUD Act to demand the data. If Apple really cared about privacy, they would have closed that hole long ago.
Do you never install software on your desktop computer?